The present invention relates to thixotropic cement compositions.
Thixotropic cement is a cement slurry which will develop a low viscosity in turbulent flow or upon agitation, but which exhibits a high viscosity upon setting. This transition is reversible when the shear or agitation is removed. Cements having thixotropic characteristics have a wider application of usage than those lacking this characteristic. Thixotropic cement compositions have utility in situations where it is desirable to pump the cement to the point of application and yet have the cement exhibit the characteristics of a still cement mortar when in use. Two examples of such situations are patching roadways having a steep incline and applying key grouting and floor filling. In each of these situations, it is desirable to pump the cement to the point of application and yet have the cement remain in place once it is positioned.
Thixotropic cement compositions are known. U.S. Pat. Nos 3,959,003 and 3,804,174 disclose a cementing composition for oil and gas wells in which a complex formed by the reaction of a salt of a polyvalent metal with a water-soluble cellulose ether is used as an additive to impart thixotropic properties to the cement. U.S. Pat. No. 3,847,635 teaches that cementitious mixtures of alpha calcium sulfate hemihydrate, portland cement and a dispersing agent are rendered thixotropic by the addition of a small amount of crystallized magnesium sulfate. A thixotropic cement composition comprising water, hydraulic cement, a titanium chelate cross-linking agent and a water-soluble cross-linkable resin such as cellulose ether is disclosed in U.S. Pat. No. 4,524,828. U.S. Pat. No. 4,415,367 discloses that cement slurries comprising iron (II) sulfate, aluminum sulfate, a hydraulic cement and water are pumpable and thixotropic.
Existing thixotropic cement compositions do not possess all the characteristics needed for various applications. Thus, thixotropic cement compositions which are very shear thinning, which maintain their shape when at rest and which do not result in the separation of water from the composition upon standing are needed.